Hydraulic prop



March 22, 1966 W, W|| KEN| 0H ETAL 3,241,801

HYDRAULIC PROP Filed NOV. 50, 1964 United States Patent O M 3,241,801 HYDRAULC PR01 Wilhelm Willrenloh, Duisburg-Wanheim, and Erich lager, Duisburg-Neudorf, Germany, assignors to Rheinstahl Wanheim G.m.h.H., Duisburg-Wanheim, Germany Filed Nov. 3), 1964, Ser. No. 414,541 Claims priority, appiication Germany, Nov. 29, 1963, R 36,68)

14 Claims. (Cl. 24S- 354) The present invention relates to extensible and contractible hydraulic props. More particularly, the invention relates to an improved multiastage hydraulic prop which may be utilized as a separate pit prop or as one of a series of pit props in a walking mine roof support to prevent cave-in of underground excavations.

It is an important object of the invention to provide a multi-stage hydraulic prop which is constructed and assembled in such a way that each of its stages offers the same or substantially the same resistance to contraction.

Another object of the invention is to provide a hydraulic prop of the just outlined characteristics wherein each stage may be shifted with reference to the other stage or stages to thereby lengthen the prop in response to admission of hydraulic fiuid to a single pressure chamber of the Yprop and wherein a single relief valve suffices to protect the prop from undue stresses.

A further object of the invention is to provide a hydraulic pit prop which may be assembled with similar props to form the roof supporting structure of a walking mine roof support, which may be manipulated by remote control, which may be constructed in any desired size, and which may comprise two or more relatively movable stages to insure that its length may be varied within a desired range.

An additional object of the instant invention is to provide a pit prop whose resistance to construction (shortening) remains unchanged regardless of the momentary length thereof and which consists of a small number of simple, rugged and easily connectible or disassemblable parts.

A further object of the present invention is to provide a very simple, rugged and reliable two-stage pit prop.

A concomitant object Iof the invention is to provide a pit prop which may be readily installed in many types of existing mine roof supports and which is equally useful as an independent roof-supporting or propping unit.

Still another object of the invention is to provide a hydraulic multi-stage prop which is capable of resisting exceptionally high compressive stresses such as will arise when the prop is utilized to prevent cave-in in underground excavations.

A further object of the invention is to provide a pit prop which may be extended to its full length within a short period of time and which may be rapidly contracted to be separable from a mine roof when the operator desires to transfer the prop to a different position -or to ad- Vance the walking mine r-oof support toward the mine face.

Brieiiy stated, one feature of the present invention resides in a provision of an extensible and contractible hydraulic prop which comprises a first tube, at least one first starge including a second tube having a portion reciprocably and sealingly telescoped into the first tube, and a second stage including a third tube having a portion reciprocably and sealingly telescoped into the second tube. The prop is provided with a single pressure chamber and the second stage comprises a piston which is located at one end of the pressure chamber. Each stage comprises a plurality of effective surfaces which are acted upon by the hydraulic fluid when the length of the prop is being changed in response to admission 3,241,801 Patented Mar. 22, 1966 of hydraulic fluid into the pressure chamber, and the combined cross-sectional area of such surfaces in the second stage at least approximates the cross-sectional area of the interior of the first tube. The prop will operate properly with a single relief valve and the combined cross-sectional area of effective surfaces in the rst stage preferably approximates or equals the combined cross-sectional area of effective sur-faces in the second stage to insure that the prop offers an unchanging resistance to contraction regardless of the momentary axial position of tubes in the rst and second stages. When the prop is to be extended, the hydraulic fluid which is admitted into the pressure chamber acts upon the piston in a sense to expel the third tube from the second tube.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved prop itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understod upon perusal .of the following detailed description of a specic embodiment with reference to the accompanying drawing the single illustration of which is an axial section through a partially extended two-stage pit prop which is constructed in accordance with the present invention.

Referring to the drawing, there is shown an extensible and contractible hydraulic prop which comprises an outer tube 1. The tube 1 is stationary and comprises a lower end which is closed by a sole plate 1a. This sole plate may engage the oor of an underground excavation when the prop is used to prevent cave-in of the mine roof or when the prop forms part of a so-called walking or travelling mine roof support. The sole plate 1a is preferably welded to the lower end of the outer tube 1 and the upper end of this tube is open so that it may receive a second tube 2 which forms part of the first stage of the prop and whose lower end is provided with an annular portion 1t] which constitutes a plunger and is slidably telescoped into the outer tube 1. The plunger 10 is provided with a U-packing 11 which is in sealing engagement with the internal surface of the outer tube 1. The second stage of the prop comprises a third tube 3 whose lower end is provided with an annular portion 12 forming a plunger provided with a U-packing 13 which is slidable along the internal sur-face of the second tube 2. The third pipe 3 extends through and beyond the open upper end of the second pipe 2. The upper end portion 3a of the pipe 3 carries a roof-engaging shield 3b which is preferably articulately secured to the end portion 3a and comes in direct engagement with the mine roof when the .prop of the present invention is used as a pit prop. If the prop forms part of a walking mine roof support, the shield 3b is preferably coupled to the shields of the other props which form part of the same mine roof support.

The open upper ends of the tubes 1 and 2 are provided with sealing sleeves 4, 4 whereby the sleeve 4 surrounds a median portion of the tube 2 and the sleeve 4' surrounds a median portion of the tube 3. Each of these sleeves carries a slide ring 5 which engages the peripheral surface of the respective tube to prevent entry of foreign matter into the prop. The connection between the sleeve 4 and the open upper end of the outer tube 1 comprises at least one horizontal coupling pin 4a which is recessed into the peripheral surface of the tube 1 and is accessible through a cutout 4b provided in the sleeve 4. The connection Ibetween the sleeve 4 and the open upper end of the tube 2 is of identical construction.

The tube 3 comprises a header 6 which is welded to and is located at a level below the upper end portion 3a. This header is provided with a first inlet 7 which serves to admit a hydraulic fluid in the direction indicated by `an arrow 7a, such fluid serving to contract the prop by causing retraction of the tube 3 into the tube 2. A second inlet 8 of the header 6 serves to admit hydraulic fluid in a direction indicated by arrow 8a for the purpose of extendingy the prop, Le., for expelling the tube 2 from the tube 1 and for expelling the tube 3 from the tube 2.

The header 6 is welded to a downwardly extending tubular piston rod 9 which projects into the interior of the tube 2 and carries at its lower end a piston 14. This piston is provided with a U-packing which is slidable in a vertical cylinder 16. The cylinder 16 is received with clearance in the lower portion of the tube 3 and extends into the tube 2. The upper end of the cylinder 16 is provided with an annular piston 17 which surrounds the piston rod 9 and accommodates an internal sealing ring 18 which seals the upper end of a retraction chamber 23 extending between the pistons 14, 17 and surrounding the lower-portion of the piston rod 9. The piston 14 and the sole plate 1a define between themselves a pressure chamber 23a which is surrounded by the lower portion of the cylinder 16. The inlet 7 communicates with the retraction chamber 23 through the interior of the piston rod 9 and through one or more radial ports 9a provided at the lower end of the piston rod just above the piston 14. The pressure chamber 23a communicates with the inlet 8 through the interior of the third tube 3, through an annular clearance 20 between the tube 3 and cylinder 16, through an annular compartment 20a between the tube 2 and cylinder 16, through an annular clearance 21 between the cylinder 16 and plunger 10, and through one or more radial ports 22 provided in the lower end face of the cylinder 16. It will be noted that the lower end of the cylinder 16 is open.

The motion transmitting connection between the lower end of the cylinder 16 and the second tube 2 comprises a pair of annular collars 19, 19a provided on the cylinder above and below the plunger 10. When the fluid is admitted to the undersurface of the plunger 10, the tube 2 will begin to move upwardly and an annular shoulder 10a of the plunger 10 will entrain the upper collar 19 so that the tube 2 and cylinder 16 move as a unit. When the tube 2 moves downwardly, the plunger 10 entrains the collar 19a.

The prop is provided with a valve unit V having a suitable fiuid supply pump P by which fluid Linder pressure is admitted to the chamber 23a to thereby lengthen the prop, having furthermore a suitable relief valve 8b to limit the pressure, which `can be built up in the chamber 23a to thereby protect the prop from undue stresses, and having a suitable release valve 8c which may be, for instance, manually operated to release the pressure in the chamber 23a so that the prop may be contracted and transferred to the next position in the underground mining room. When the prop of the present invention is used as a self-contained unit, the valve unit V may be arranged in or at the header 6 as actually shown in the drawing. However, when the prop forms part of a walking mine roof support, the valve unit V may be mounted at -a distance from the prop so that several props may be controlled by a common valve unit.

If the prop is to be shortened, i.e. if the tube 3 is to be retracted into the tube 2, the operator firstly operates the above-mentioned release valve 8c by moving its actuating member 8e to the brokenline position 8e so that the passage 8 communicates with an outlet Sd through which the hydraulic fluid may be expelled from the chambers or compartments 2t), 20a, 21 and 23a via the passage 8. Then the operator will admit hydraulic fiuid through the inlet 7 (arrow 7a) so that the fiuid fiows through the interior of the piston rod 9 and through the ports 9a to enter the retraction chamber 23. Such fiuid acts against the surfaces 14a, 17a of the pistons 14, 17 and causes the tube 3 to descend. When its actuating member 8e is moved to the position 8e, the valve 8c seals the passage 8 from the pump P and from the outlet 3d.

The cross-sectional areas of effective surfaces in the two stages of the prop are selected in such a way that, when the prop is being extended, the third tube 3 begins to rise in the first step and the tube 2 begins to rise as soon as the tube 3 reaches the upper end of its stroke. However, when the shield 3b is subjected to stresses which tend to shorten the prop, the second tube 2 will descend first While the third tube 3 remains in fully extended position. Such dimensioning of effective surfaces in the two stages of the prop is of advantage because the prop may be shortened by the full length of the stroke of the tube 3 regardless of the axial position of the tube 2 with reference to the tube 1. In other words, and assuming that the second tube 2 is halfway expelled from the outer tube 1, the operator can shorten the prop by the full length of the stroke of the tube 3 by admitting a fiuid through the inlet 7. Therefore, the shield 3b may be separated from the mine roof regardless of the axial position of the tube 2 so that the prop may be shifted to a different position or that the walking mine roof support may be advanced toward the mine face.

The combined effective surface F3 of the second stage (tube 3) is composed of three surfaces including a first surface F3 (this is the annular surface at the underside of the annular plunger 12 at the lower end of the tube 3), a second surface F3 (this is the annular surface at the underside of t'ne header 6) and a third surface F3'" (this is the surface at the underside of the lower piston 14). Thus, the underside F3 of the piston 14 forms part of the effective surface F3 of the third stage whereby the total cross-sectional area of the surface F3 at least approximates but preferably equals the cross-sectional area of the interior of theouter tube 1, i.e., the area of the surface F3 equals or approximates the area within a circle whose diameter corresponds to the internal diameter of the tube 1.

The combined effective surface F2 of the first stage (tube 2) equals the surface F2 (this is the annular surface at the upper side of the piston 17) minus the surface F2 (this is the annular surface at the underside of the plunger 10 provided at the lower end of the second tube 2). As a rule, the cross-sectional area of the surface F2 will exceed very little (for example, by a few cm2) the cross-sectional area of the surface F2. Consequently, when the hydraulic fluid is admitted through the inlet 8, the pressure is distributed in such a way that the cylinder 16 first moves to the lower end position shown in the drawing and begins to rise with the tube 2 only at the time when the tube 3 has been lifted to its upper end position, i.e., when the surfaces 14a, 17a are in actual abutment with each other. Inversely, when the fluid is entrapped in the pressure chamber 23a and the shield 3b transmits such stresses which cause a contraction (shortening) of the prop, the second tube 2 will yield before the tube 3 yields so that the plunger 10 begins to travel toward the sole plate la while the tube 3 remains in fully extended position. Of course, tube 3 will share the downward movement of the tube 2 but will not change its axial position with reference thereto.

When the prop is to be extended so as to move the shield 3b toward the mine roof, the operator admits hydraulic fluid through the inlet 8 (arrow 8a). The fiuid acts against the effective surface 'F3 by acting against the surfaces Fa, F3", F3m whereby the tube 3 begins to move upwardly and the piston 14 expels fluid from the retraction chamber 23. Such fiuid returns through the ports 9a to escape via inlet 7. The tube 2 remains stationary because the area of the surface F2" is greater than the area of the surface F2', i.e., the cylinder 16 is pressed into abutment with the sole plate 1a. However, once the surface 14a of the piston 14 comes in abutment with the surface 17a of the piston 17, the surface F3" is added to the surface F2 and the tube 2 begins to move to the upper end position. Such movement of the tube 2 is shared by the cylinder 16 because t-he shoulder 10a of the plunger 10 abuts against the underside of the collar 19.

A very important advantage of the improved prop is that its stages offer a substantially unchanging :resistance to contraction regardless of the momentary length of the prop. In other words, the resistance which the prop 4offers to contraction is the same when the tube 2 and/ or 3 is partly or fully extended. A single relief valve will sufiice to control the escape of fluid in response to contraction of the prop and a single pressure chamber suffices to extend the prop to its full length.

Instead of connecting the retraction chamber 23 with a source of hydraulic fluid by means of a fluid supply pipe or a fiuid supply piston connected with the fiuid supply pipe and provided with a manually or otherwise operated valve 7b, the ports 9a in the piston rod 9 and the inlet 7 in the header 6 may be closed so that the chamber 23 is sealed from the atmosphere. The charnber Z3 is filled with air and such air undergoes compression in response to admission of hydraulic fluid into the chamber 23a, i.e., in response to upward movement of the piston 14 in a sense to reduce the volume of the retraction chamber 23. The thus entrapped air forms a cushion and stores energy which is released when the release valve 8c is operated to connect the outlet 8d with the cylinder chamber 23a via passages 8, so that the hydraulic fluid may be expelled from the cylinder chamber 23a. When this valve 3c has been opened, the expanding air in the chamber 23 rapidly retracts the tube 3 into the tube 2 or the tube 1 to shorten the prop. However, it is normally preferred to connect the inlet 7 with a suitable source of compressed hydraulic fiuid, particularly when the prop forms part of a walking mine roof support.

It will be noted that, due to the aforementioned specific relationship between the areas of the surfaces F2' and F2, the prop need not be provided with means for retracting the first stage (tube 2) because the tube 2 will be retracted in the first step whenever the magnitude of stresses acting on the shield 3b is such that the length of the prop rnust be reduced. In other words, it suffices to provide means for retracting the second stage (tube 3). The effective surface F3 of the second stage is enlarged by the surface F3" of the lower piston 14 which contributes considerably to the resistance which the prop offers to contraction without necessitating the provision of large-diameter tubes. In addition, and since the piston 14 forms part of the means for shortening the prop, the effective surface F3 is enlarged without necessitating the provision of additional parts for such enlargement.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the appended claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. An extensible multi-stage hydraulic prop, comprising a first tube; at least one first stage including a second tube having a portion reciprocably telescoped into said first tube; and a second stage including a third tube having a portion reciprocably telescoped into said second tube, said prop defining a single pressure chamber and said second stage comprising a piston located at one end of said chamber, each of said stages having an effective surface which is acted upon by fluid when the prop is being extended in response to admission of hydraulic fluid into said chamber, the cross-sectional area of each effective surface being substantially the same so that the prop offers a substantially constant resistance to stresses which tend to contract the same and the cross-sectional area of the effective surface in said second stage at least approximating the cross-sectional area of the internal space of said first tube.

2. An extensible hydraulic prop as set forth in claim 1, further comprising a single relief valve for regulating the outflow of hydraulic fiuid from said pressure chamber.

3. An extensible and contractible hydraulic prop as set forth in claim 1, wherein said second stage further comprises a cylinder received in said third pipe and slidably receiving said piston, means connecting the cylinder for reciprocatory movement with said second tube, and a second piston secured to said cylinder and defining with said first named piston a retraction chamber arranged to receive pressure fiuid when said third tube is to be retracted into said second tube.

4. An extensible and contractible hydraulic prop as set forth in claim 3, wherein said second stage further comprises a piston rod connected with said first named piston and received in said third tube, and a header connecting said piston rod to said third tube, said header having an inlet for admitting hydraulic fluid into said pressure chamber.

5. An extensible and contractible hydraulic prop as set forth in claim 4, wherein said header comprises a second inlet for admitting a fluid to said retraction chamber.

6. An extensible and contractible hydraulic prop as set forth in claim 5, wherein said piston rod is a tubular body and is provided with port means connecting its interior with said retraction chamber, said second inlet communicating with the interior of said tubular body.

7. An extensible and contractible hydraulic prop as set forth in claim 1, wherein the cross-sectional areas of said effective surfaces are selected in such a way that, on admission of pressure fluid into said chamber, the third tube is expelled from the second tube before the second tube is expelled from the first tube.

8. An extensible and contractible hydraulic prop, comprising a first tube having an open end and a closed end; a second tube extending through said open end and having an annular end portion reciprocably telescoped into said first tube, said second tube having an open end; a third tube extending through the open end of said second tube and comprising an annular end portion reciprocably telescoped into said second tube; a cylinder received in said third tube and coupled to said second tube; a piston rod connected with said third tube and extending into said cylinder; a first piston connected with said piston rod and reciprocably telescoped into said cylinder so as to define in said cylinder a pressure chamber which extends to said closed end; a second piston provided on said cylinder and slidably surrounding said piston rod so as to define with said first piston a retraction chamber which is separated from said pressure chamber by said first piston; first inlet means for admitting a hydraulic fluid into said pressure chamber via said third tube and around said cylinder; and means for regulating the fiow of fluid into and from said retraction chamber.

9. An extensible and contractible hydraulic prop, comprising an outer tube having an open end and a closed end; a second tube extending through said open end and having an annular plunger reciprocably telescoped into said outer tube, said second tube having an open end which is distant from said closed end; a third tube extending through the open end of said second tube and having an annular plunger reciprocably telescoped into said second tube, each of said plungers having an annular surface facing said closed end; an open-ended cylinder received with clearance in the plunger of said third tube and adjacent to said closed end when the prop is contracted; motion transmitting means for coupling said cylinder to said second tube; a first piston provided on said cylinder and spaced from said closed end, said piston having an annular surface facing away from said closed end; a tubular piston rod reciprocably received in said first piston; a second piston secured to said piston rod intermediate said first piston and said closed end so as to divide the interior of said cylinder into a retraction charnber extending between said pistons and a pressure chamber extending between said second piston and said closed end, said second piston having a surface facing said closed end; and a header connecting said piston rod to said tube, said header having first inlet means for admitting a hydraulic fluid into said third tube whereby such fluid flows around said cylinder and into said first tube intermediate the closed end of said first tube and the surface of said first named plunger to enter said pressure chamber through port means provided in said cylinder to act upon the surfaces of said second piston and said plungers and to respectively expel said third and second tubes from said second and first tubes, said header further having a second inlet through which a fluid may be admitted into said retraction chamber via said piston rod and port means provided in the piston rod whereby such fluid acts upon said pistons to retract said third tube into said second tube.

10. A hydraulic prop as set forth in claim 9, wherein said header is provided with an annular surface surrounding said piston rod and facing said closed end, the combined area of the surface on said header, of the surface on the plunger of said third tube and of the surface on said second piston at least approximating the cross-sectional area of the internal space in said first tube.

11. A hydraulic prop as set forth in claim 10, wherein the area of the surface on said first piston exceeds at least slightly the area of the surface on the plunger of said second tube.

12. An extensible and contractible hydraulic pit prop adapted to be installed between the floor and the roof of an underground excavation, comprising an outer tube having an open end and a closed end provided with a floorengaging sole plate; a second tube extending through said open end and having an annular plunger reciprocably telescoped into said outer tube, said second tube having an open end which is distant from said closed end; a third tube extending through the open end of said second tube and having an annular plunger reciprocably telescoped into said second tube, each of said plungers having an annular surface facing said closed end and said third tube comprising an upper end portion provided with a roofengaging member; an open-ended cylinder received with clearance in the plunger of said third tube and adjacent to said closed end when the prop is contracted; motion transmitting means for coupling said cylinder to said second tube; a first piston provided on said cylinder and spaced from said closed end, said piston having an annular surface facing away from said closed end; a tubular piston rod reciprocably received in said first piston; a second piston secured to said piston rod intermediate said first piston and said closed end so as to divide the interior of said cylinder into a retraction chamber extending between said pistons and a pressure chamber extending between said second piston and said closed end, said second piston having a surface facing said closed end; and a header connecting said piston rod to said tube, said header having first inlet means for admitting a hydraulic fluid into said third tube whereby such fluid flows around said cylinder and into said first tube intermediate the closed end of said first tube and the surface of said first named plunger to enter said pressure chamber through port means provided in said cylinder to act upon the surface of said second piston and said plungers and to respectively expel said third and second tubes from said second and first tubes, said header further having a second inlet through which a fluid may be admitted into said retraction chamber via said piston rod and port means provided in the piston rod whereby such fluid acts upon said pistons to retract said third tube into said second tube.

13. A hydraulic pit prop as set forth in claim 12, further comprising a first sleeve provided at the open end of said first tube and comprising means for sealingly engaging said second tube to prevent entry of foreign matter into said outer tube, and a second sleeve provided at the open end of said second tube and sealingly engaging said third tube to prevent entry of foreign matter into said second tube.

14. A hydraulic pit prop as set forth in claim 12, where in said motion transmitting means comprises flange means provided on said cylinder and located in the path of said first named plunger.

References Cited by the Examiner UNITED STATES PATENTS 1,343,862 10/1963 France.

CLAUDE A. LE ROY, Primary Examiner. 

1. AN EXTENSIBLE MULTI-STAGE HYDRAULIC PROP, COMPRISING A FIRST TUBE; AT LEAST ONE FIRST STAGE INCLUDING A SECOND TUBE HAVING A PORTION RECIPROCABLY TELESCOPED INTO SAID FIRST TUBE; AND A SECOND STAGE INCLUDING A THIRD TUBE HAVING A PORTION RECIPROCABLY TELESCOPED INTO SAID SECOND TUBE, SAID PROP DEFINING A SINGLE PRESSURE CHAMBER AND SAID SECOND STAGE COMPRISING A PISTON LOCATED AT ONE END OF SAID CHAMBER, EACH OF SAID STAGES HAVING AN EFFECTIVE SURFACE WHICH IS ACTED UPON BY FLUID WHEN THE PROP IS BEING EXTENDED IN RESPONSE TO ADMISSION OF HYDRAULIC FLUID INTO SAID CHAMBER, THE CROSS-SECTIONAL AREA OF EACH EFFECTIVE SURFACE BEING SUBSTANTIALLY THE SAME SO THAT THE PROP OFFERS A SUBSTANTIALLY CONSTANT RESISTANCE TO STRESSES WHICH END TO CONTRACT THE SAME AND THE CROSS-SECTIONAL AREA OF THE EFFECTIVE SURFACE IN SAID SECOND STAGE AT LEAST APPROXIMATING THE CROSS-SECTIONAL AREA OF THE INTERNAL SPACE OF SAID FIRST TUBE. 